By Timothy R. Donahue, P.E.
Generally speaking, for a given structure, the higher the seismic response factor (R) value is, the more ductile the structure is and the lower the total seismic load acting on the building. With this concept in mind, one might conclude that reducing the seismic load acting on a building by selecting a more ductile seismic force restraint system (SFRS) with a higher R value would ultimately lower the material cost; however, when evaluating the overall cost implications for what it takes to achieve the increased ductility, the cost savings may not always be realized. This is primarily due to the requirements of overstrength factors in the design and detailing of the straps and other protected components of the SFRS with an R greater than 3.
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